The additional vibration from unbalanced props also does not do your radio equipment any good. Balsa fuselages are better at absorbing vibration than plastics or composites but balancing the prop and isolating the receiver with foam is still a good idea for your receiver.

Any metal on metal vibration can also cause radio interference particularly with AM systems. So reducing vibration and eliminating the potential for metal to metal contact (such as the throttle pushrod contacting the engine) will improve the reliability of your radio equipment.

And I'd agree you can balance a prop with a piece of tubing but if it isn't accurately balancing the prop, (and at 16,000 rpm accuracy counts) you are not really saving any money when it leads to a crash or dead stick landing. So again, the gizmo in the hobby shop is the cheap way to do it.

One more thought on vibration...even with the propeller balanced, the engine/prop combo and the varirous parts of the airframe will still vibrate and resonate at certain frequencies. When you get a prop that does what you want it to do, do a ground check to ensure there are no rpm ranges where you encounter sympathetic resonance.

If for example the horizontal stab is vibrating in harmony with the engine at a certain rpm, you will get a much larger amplitude in the vibrations. This can cause the airframe part in question to fail or at least will cause the joints to be highly stressed. (A good argument for using more flexible epoxy rather than CA for connencting firewalls and tail surfaces to the fuselage.) The increased amplitude will also cause a higher level of vibration though out the airframe with potential radio and fuel problems resulting. Theoretically the propeller could also fail, but I've never seen this happen in an R/C aircraft.

Normally if this is occurring, the airframe part will "buzz" or even visibly vibrate. If it occurs make a note to avoid operating in that rpm range in flight. It's normally not a big deal as long as it is not occurring at a throttle setting you use a lot (ie for take-off, climb, cruise or decent and approach to landing). If it is occurring in a critical range, you can switch to a different brand, pitch, or diameter of propeller and it may resolve as the vibration frequencies will be different with the differrent prop.